Purpose: :
To determine the mechanisms by which subconjunctival insulinand systemic glucose reduction with phloridzin, a sodium-linkedglucose transporter inhibitor, influence a validated mRNA biomarkerpanel and immunohistochemical markers for diabetic retinopathy.

Methods: :
Diabetic and non-diabetic control male Sprague-Dawley rats receivedsystemic insulin by subcutaneous implants, subconjunctival injectionsof insulin (0.03 U/100 g body weight), or intraperitoneal injectionsof phloridzin (0.2 mg/100 g body weight) twice daily for thelast 4 days of a 3-month experiment. Retinas were analyzed forexpression mRNAs belonging to a 15-gene biomarker panel we previouslydemonstrated to be altered in experimental diabetic retinopathy.Assay-On-Demand gene specific primers and probes and the 2-ΔΔCtanalysis method was used to quantify relative mRNA contentsusing ß-actin as an endogenous control. Immunohistochemistrywith a GFAP-specific antibody was used to determine the effectof both treatments on diabetic-induced retinal gliosis.

Results: :
Nine of 15 diabetes-induced biomarker changes were reversedafter systemic insulin treatment. Subconjunctival insulin administrationreversed these same changes, plus that of one additional genein the biomarker panel. Lowering systemic glucose by phloridzintreatment reversed 8 biomarker changes. Only 5 biomarker reversalswere common to both local insulin and phloridzin treatment sets.Surprisingly, combined treatment with local insulin and phloridzinreversed the responses of all 15 genes. Whereas local insulinpartially reduced glial cell activation, phloridzin fully blockedthis response to diabetes.

Conclusions: :
These data indicate that ocular insulin administration and systemicglucose reduction each have direct and distinct effects on retinalgene expression, and suggest that manipulating both hormoneand nutrient levels may influence the development of early diabeticretinopathy.